Frustrated that his (and fellow Googler Peter Norvig’s) Stanford artificial intelligence class only reached 200 students, they put up a website offering an online version. They got few takers. Then he mentioned the online course at a conference with 80 attendees and 80 people signed up. On a Friday, he sent an offer to the mailing list of a top AI association. On Saturday morning he had 3,000 sign-ups—by Monday morning, 14,000.

In the midst of this, there was a slight hitch, Mr. Thrun says. “I had forgotten to tell Stanford about it. There was my authority problem. Stanford said ‘If you give the same exams and the same certificate of completion [as Stanford does], then you are really messing with what certificates really are. People are going to go out with the certificates and ask for admission [at the university] and how do we even know who they really are?’ And I said: I. Don’t. Care.”

In the end, there were 160,000 people signed up, from every country in the world, he says, except North Korea. Rather than tape boring lectures, the professors asked students to solve problems and then the next course video would discuss solutions. Mr. Thrun broke the rules again. Twenty-three thousand people finished the course. Of his 200 Stanford students, 30 attended lectures and the other 170 took it online. The top 410 performers on exams were online students. The first Stanford student was No. 411.

Mr. Thrun’s cost was basically $1 per student per class. That’s on the order of 1,000 times less per pupil than for a K-12 or a college education—way more than the rule of thumb in Silicon Valley that you need a 10 times cost advantage to drive change.

So Mr. Thrun set up a company, Udacity, that joins many other companies attacking the problem of how to deliver the optimal online education. “What I see is democratizing education will change everything,” he says. “I have an unbelievable passion about this. We will reach students that have never been reached. I can give my love of learning to other people. I’ve stumbled into the most amazing Wonderland. I’ve taken the red pill and seen how deep Wonderland is.”

“But Wonderland is also crazy!” I interrupt.

“So?” . . . I ask why he always takes on these quantum changes instead of trying something incremental. “That’s what Google taught me. Aim higher. Udacity is my playground—to radically experiment and find out. I’ve seen the light.”

Now Mr. Thrun is talking like a true Silicon Valley entrepreneur. “The AI class was the first light. Online education will way exceed the best education today. And cheaper. If this works, we can rapidly accelerate the progress of society and the world. If you think Facebook is neat, wait five to 10 years. So many open problems will be solved.”

I’ve met a few others like Sebastian Thrun. When you ask them why they took on a huge challenge, they ask: Why not?

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